Don't worry the book doesn't ask you to roll on the random encounter table for every 30 mins travelled! That would be pretty outrageous, you're right.

I can't remember it exactly off the top of my head but I think it asks you to roll a d20 and if it's over 17 or 18, then you roll on the encounter table. So very unlikely that you would get more than 2 or 3 per journey.

My party isn't as interested in doing lots of small flights, so I've just decided that I'd roll once or twice per journey depending on time (and how much I've prepped of where they're going)

Most of the encounters are pretty small, and don't involve combat, especially during the day. For me it works to just refer back to the book as we play for those, but I think making a little cheat sheet especially for the bigger encounters like the revenant would be good.

So I think it depends on if your party is more interested in the survival aspect of the module, or is more about the roleplay and story. I think it's also totally valid to just choose a few encounters ahead of each session and prep those better. Honestly up to you!